The present invention relates generally to the field of substrate processing equipment. More particularly, the present invention relates to a method and apparatus for controlling the temperature of substrates, such as semiconductor substrates, used in the formation of integrated circuits.
Modern integrated circuits (ICs) contain millions of individual elements that are formed by patterning the materials, such as silicon, metal and/or dielectric layers, that make up the integrated circuit to sizes that are small fractions of a micrometer. A number of steps associated with the fabrication of integrated circuits include heating the semiconductor substrate upon which the ICs are formed. One example of a heating step includes curing a photoresist film prior to a photolithography process. A photoresist film can be cured, for example, by placing a semiconductor substrate having an uncured photoresist film formed thereon on a bake plate and heating the plate to a sufficiently high temperature for a predetermined period of time.
Over the years there has been a strong push within the semiconductor industry to shrink the size of semiconductor devices. The reduced feature sizes have caused the industry's tolerance to process variability to shrink, which in turn, has resulted in semiconductor manufacturing specifications having more stringent requirements for process uniformity and repeatability. One manifestation of these more stringent requirements is the desirability to precisely control the temperature of a semiconductor substrate in a bake plate heating operation such as the photoresist curing operation just described.
To this end, the industry has developed heater plates that include multiple heater elements arranged in different zones. Such an arrangement allowed one zone of the heater plate to be heated at a slightly higher temperature than other zones to compensate for temperature nonuniformities that may occur between different points on the semiconductor substrate. FIG. 1 is a top plan view of an example of a previously known bake plate that includes six different electrically independently heating zones. As shown in FIG. 1, bake plate 10 includes six independent heater zones 121-126 along with a corresponding number of temperature sensors 141-146, one for each of the heater zones 121-126.
Depending on the type of temperature sensor used, each sensor and independent heater zone requires at least three separate wires and often five or more separate wires (e.g., a five wire arrangement may use two wires for AC power connections to the heater element and three wires for connections to the sensor). Between the multiple zones used in many zone heater bake plates and the fact that each zone often includes its own temperature sensor having multiple dedicated wires, it can be appreciated that a zone heater may readily have twenty, thirty or even more wires extending from it. Effectively and efficiently managing such a large number of wires presents challenges.